Development of the Characterization Methods Without Electrothermal Feedback for TES Bolometers for CMB Measurements

Abstract

Superconducting Transition-Edge Sensor (TES) bolometers are used for cosmic microwave background (CMB) observations. We used a testbed to evaluate the thermal performance of TES bolometers in regard to the saturation power $P_{\mathrm {sat}}$ and intrinsic thermal time constant $\tau _0$. We developed an evaluation method that is complementary to methods with electrothermal feedback. In our method, the antenna termination resistor of the bolometer is directly biased with DC or AC electric power to simulate optical power, and the TES is biased with small power, which allows $P_{\mathrm {sat}}$ and $\tau _0$ to be determined without contribution from the negative electrothermal feedback. We describe the method and results of the measurement using it. We evaluated $P_{\mathrm {sat}}$ of five samples by applying DC power and confirmed the overall trend between $P_{\mathrm {sat}}$ and the inverse leg length. We evaluated $\tau _0$ of the samples by applying DC plus AC power, and the measured value was reasonable in consideration of the expected values of other TES parameters. This evaluation method enables us to verify whether a TES has been fabricated with the designed values and to provide feedback for fabrication for future CMB observations.